Bio-inspired wooden actuators for large scale applications.

Markus Rüggeberg,Ingo Burgert,Dario Pisignano

doi:10.1371/journal.pone.0120718

Markus Rüggeberg, Ingo Burgert + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0120718

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Abstract

Implementing programmable actuation into materials and structures is a major topic in the field of smart materials. In particular the bilayer principle has been employed to develop actuators that respond to various kinds of stimuli. A multitude of small scale applications down to micrometer size have been developed, but up-scaling remains challenging due to either limitations in mechanical stiffness of the material or in the manufacturing processes. Here, we demonstrate the actuation of wooden bilayers in response to changes in relative humidity, making use of the high material stiffness and a good machinability to reach large scale actuation and application. Amplitude and response time of the actuation were measured and can be predicted and controlled by adapting the geometry and the constitution of the bilayers. Field tests in full weathering conditions revealed long-term stability of the actuation. The potential of the concept is shown by a first demonstrator. With the sensor and actuator intrinsically incorporated in the wooden bilayers, the daily change in relative humidity is exploited for an autonomous and solar powered movement of a tracker for solar modules.

Highlights

The design of advanced functional materials with implemented stimuli-responsiveness, programmable and reversible actuation, or shape-memory effect [1,2,3] is one of the most rapidly developing fields in materials science
Actuation of bilayers have been demonstrated with materials that are responsive to other external stimuli such as relative humidity [6,7], pH [8,9], PLOS ONE | DOI:10.1371/journal.pone
The differential swelling coefficient was determined by tracking the dimensional changes of the marked spruce and beech strips included in the experiment with step-wise change of relative humidity

Summary

Introduction

The design of advanced functional materials with implemented stimuli-responsiveness, programmable and reversible actuation, or shape-memory effect [1,2,3] is one of the most rapidly developing fields in materials science. The differential swelling coefficient was determined by tracking the dimensional changes of the marked spruce and beech strips included in the experiment with step-wise change of relative humidity (see above). The experimentally derived specific curvatures which were reached 24 hours after transfer matches with those which were calculated using the theory of Timoshenko (Fig. 2e), which confirms the results of preceding studies on moisture induced actuation of polymer bilayers [6].

Results

Conclusion